Conventionally, miniature unmanned aerial vehicles (UAVs) which are typified by unmanned helicopters for industrial use have been expensive and hard to obtain and manipulative skills have been needed to make them fly stably. However, the prices of such UAVs have fallen recently, because acceleration sensors and angular velocity sensors, which have high performance and are easy to handle, as well as microcontrollers or the like have become available at moderate prices, and in addition maneuverability has improved dramatically, since many operations to control and manipulate the UAV airframe have been automated. Against this background, attempts are now made to apply, especially, miniature multicopters to diverse missions in a wide range of fields, not only for hobby purposes.
A multicopter is one type of helicopter in which a plurality of rotors are installed and is a rotorcraft flying, while keeping balance of the airframe by controlling the rotating speed of each of these rotors. Since a multicopter can employ a propeller with a simpler structure than that of a helicopter, the multicopter is easy to maintain and its airframe can be built at comparatively low cost.